Viscous Flow Past a Circular Cylinder Below a Free Surface

Flow past a circular cylinder close to a free surface at low Reynolds and large Froude numbers is investigated numerically using the Smoothed Particle Hydrodynamics model. This mesh- less method allows for a non-diffusive computation of the free surface evolution, even while breaking and fragmentation may occur. The distance of the cylinder to the free surface, submer- gence, is varied in order to investigate the detached flow pat- terns dependence with this factor. Vorticity shed by the cylin- der, vortex generation due to free surface breaking, mixing pro- cesses, and drag and lift coefficients behavior are discussed. It has been found that, for small submergences, the classical Von Karman vortex shedding from the cylinder does not take place. In turn, moderate vortex shedding occurs, departing not from the cylinder but from vorticity generated at the free surface. This shedding takes places simultaneously with the transport of free surface fluid elements into the bulk of the fluid. It has been also found that for even smaller depth ratios, a vorticity layer remains spatially localized between the cylinder and the free surface, and a stagnation recirculating area develops behind the cylinder. Re- sults are compared with literature finding reasonable qualita- tively agreement with experimental works conducted with similar geometrical configuration but larger Reynolds number.